Patterning devices using fluorinated compounds

ABSTRACT

A method for producing a spatially patterned structure includes forming a layer of a material on at least a portion of a substructure of the spatially patterned structure, forming a barrier layer of a fluorinated material on the layer of material to provide an intermediate structure, and exposing the intermediate structure to at least one of a second material or radiation to cause at least one of a chemical change or a structural change to at least a portion of the intermediate structure. The barrier layer substantially protects the layer of the material from chemical and structural changes during the exposing. Substructures are produced according to this method.

CROSS-REFERENCE OF RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/123,678 filed Apr. 10, 2008, the entire content of which is herebyincorporated by reference.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Grant No.DE-FG02-07ER46465, awarded by DOE, and of Grant No. FA9550-06-1-0076,awarded by the USAF AFOSR.

BACKGROUND

1. Field of Invention

The current invention relates to methods of producing spatiallypatterned structures, and more particularly to methods of producingspatially patterned structures using fluorinated compounds. The currentinvention also relates to structures produced according to the methods.The current invention also relates to thin-film, lateral, organicheterojunction diodes.

2. Discussion of Related Art

Traditional photolithographic patterning has not proven useful topattern organic semiconductors, and organic materials in general,because of damage by the photoresist, developer and acetone during theprocessing (Patterning Surfaces with Functional Polymers, Zhihong Nieand Eugenia Kumacheva, Nature materials, vol. 7, (April 2008)). Severalapproaches have been used to pattern organic semiconductors ranging from(a) use of parylene as a protective layer (Patterning Pentacene OrganicThin Film Transistors, Kymissis et al, J. Vac. Sci. Technol. B 20.1,(2002)), (b) use of parylene as mechanical resist (PhotolithographicPatterning of Organic Electronic Materials, DeFranco et al, OrganicElectronics 7 (2006) 22-28) and (c) use of UV curable precursors topentacene (Flexible active-matrix displays and shift registers based onsolution-processed organic transistors, Gelinck et al, Nature Materials,Vol 3, (2004)). The approach (a) can only be used to make bottom contactcircuits and devices which have an order of magnitude lower performance.The approach (b), in addition to having the problems of approach (a),also has a problem of damage to the underlying parylene layer duringmechanical peel off of parylene. The approach (c) is limited to onlypentacene and has problems of lower mobility.

In addition, organic heterojunctions have been an extensive area ofresearch for more than two decades and have found successfulapplications in Organic Light Emitting Diodes (OLEDs), and organicphotovoltaics. While OLEDs are already on the market in displayapplications and are poised to enter the solid state lighting market inthe near future, solar cells based on organic heterojunctions still needto achieve higher efficiencies to be commercially viable. With theadvent of solar cells and OLED devices with increasingly complex deviceconfigurations and morphologies, it has become difficult to isolate andunderstand the various physical processes occurring at differentinterfaces and in the bulk at applied bias and in the presence of light.While devices based on organic heterojunctions have achieved significanttechnological milestones, the science behind them is still notcompletely understood and new techniques are needed to study the physicsof such diodes

Because of the “buried” nature of interfaces in vertical or bulkheterojunctions, there has been little attempt to study properties, suchas conductivity, dielectric constant, and morphology, on both sides ofsuch interfaces in one device.

Therefore, there remains a need for improved methods of producingspatially patterned structures and structures produced according to theimproved methods.

SUMMARY

A method for producing a spatially patterned structure according to anembodiment of the current invention includes forming a layer of amaterial on at least a portion of a substructure of the spatiallypatterned structure, forming a barrier layer of a fluorinated materialon the layer of material to provide an intermediate structure, andexposing the intermediate structure to at least one of a second materialor radiation to cause at least one of a chemical change or a structuralchange to at least a portion of the intermediate structure. The barrierlayer substantially protects the layer of the material from chemical andstructural changes during the exposing.

A method for producing a spatially patterned structure according to anembodiment of the current invention includes providing a substructure ofthe spatially patterned structure, forming a barrier layer of afluorinated material on the substructure to provide an intermediatestructure, and removing the barrier layer of fluorinated material fromthe intermediate structure. The barrier layer substantially protects atleast a portion of the substructure from chemical and structural changesduring the producing the spatially patterned structure. Substructuresaccording to some embodiments of the current invention are producedaccording to methods according to some embodiments of the currentinvention.

A diode according to an embodiment of the current invention has asubstructure, a thin film of an n-channel organic semiconductor formedon the substructure, a thin film of a p-channel organic semiconductorformed on the substructure in a position laterally displaced from thethin film of the n-type organic semiconductor so as to form a p-nheterojunction in a lateral arrangement on the substructure.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objectives and advantages will become apparent from aconsideration of the description, drawings, and examples.

FIG. 1 is a schematic illustration to demonstrate non-damagingproperties of processing methods using CYTOP and perfluorodecalin (PFD)according to some embodiments of the current invention.

FIG. 1A is schematic illustration of a method of producing a spatiallypatterned structure according to an embodiment of the current invention

FIGS. 2A and 2B show output curves for pentacene OFETs (organic fieldeffect transistors) (FIG. 2A) control samples and (FIG. 2B) after CYTOPand PFD treatment, as illustrated in FIG. 1.

FIG. 3 is a schematic illustration of a method of producing a spatiallypatterned structure according to another embodiment of the currentinvention that includes photolithography.

FIG. 4 is a schematic illustration of a method of producing a spatiallypatterned structure according to another embodiment of the currentinvention that can use the steps illustrated in FIG. 3 as an initialstage of the method.

FIGS. 5A-5F provide a schematic illustration of a method of producing aspatially patterned structure according to another embodiment of thecurrent invention that includes a solution-based printing process.

FIGS. 5G-5H provide a schematic illustration of a method of producing aspatially patterned structure according to another embodiment of thecurrent invention that includes a solution-based printing process.

FIGS. 6A-6C provide a schematic illustration of a method of producing aspatially patterned structure according to another embodiment of thecurrent invention that includes a solution-based printing process.

FIG. 7 is a schematic illustration of a method of producing a spatiallypatterned structure according to another embodiment of the currentinvention. FIG. 7 also provides a schematic illustration of a thin-film,lateral heterojunction, organic diode according to an embodiment of thecurrent invention and which can be made by the illustrated method.

FIG. 7A is a schematic illustration of a thin-film, lateralheterojunction, organic diode according to an embodiment of the currentinvention which can be made by the method of FIG. 7.

FIG. 8 shows the transfer characteristics of diode homojunctionsaccording to an embodiment of the current invention.

FIGS. 9-12 show measured diode characteristics and rectification ratiofor a NTCDI and P3HT (Rieke Metals Grade) thin-film, lateralheterojunction, organic diode according to an embodiment of the currentinvention.

FIGS. 13-16 show measured diode characteristics and rectification ratiofor a 5FPE-NTCDI with PLEXTRONICS grade high molecular weight P3HTthin-film, lateral heterojunction, organic diode according to anembodiment of the current invention.

FIG. 17 shows measured diode characteristics of a lateral diodeaccording to an embodiment of the current invention.

DETAILED DESCRIPTION

Some embodiments of the current invention are discussed in detail below.In describing embodiments, specific terminology is employed for the sakeof clarity. However, the invention is not intended to be limited to thespecific terminology so selected. A person skilled in the relevant artwill recognize that other equivalent components can be employed andother methods developed without departing from the broad concepts of thecurrent invention. All references cited herein are incorporated byreference as if each had been individually incorporated.

While none of the conventional methods mentioned above are general innature, we describe here a method of patterning materials which can beubiquitously applied to pattern, in principle, any material andcorresponding device, including devices that have spatially patternedorganic semiconductor materials. However, the general concepts of thecurrent invention are not limited to only organic semiconductor devices.Other embodiments of the current invention include inorganicsemiconductor devices and devices that include biological materials suchas bio-sensors, for example. Biological materials can include, but arenot limited to, films of proteins, lipids, DNA or other biologicalmacromolecules or other soft matter.

FIG. 1 is a schematic illustration that helps describe some concepts ofsome embodiments of the current invention. A method for producing aspatially patterned structure 100 according to an embodiment of thecurrent invention includes forming a layer of a material 102 on at leasta portion of a substructure 104 of the spatially patterned structure100. In this embodiment, the substructure 104 includes a substrate 106with a dielectric layer 108 on the substrate 106. The invention is notlimited to only this example of a substructure 104. The substructure 104can be a less or more complex substructure than the example illustrated.In this example, the layer of material 102 is an organic semiconductor(OSC), the substrate 106 is a silicon substrate, and the dielectriclayer 108 is a silicon dioxide layer. The general concepts of thecurrent invention are not limited to only these examples. The methodaccording to this embodiment of the current invention further includesforming a barrier layer of a fluorinated material 110 on the layer ofmaterial 102 to provide an intermediate structure 112. In this examplethe fluorinated material is the commercially available fluorinatedpolymer called CYTOP. Although not shown in FIG. 1, additionalprocessing steps can include adding additional layers of material andfurther chemical, photolithographic and/or additional processing. Thespecific example of FIG. 1 is provided to demonstrate that including theCYTOP layer and then removing it does not cause undesirable effects onthe resulting spatially patterned structure 100. A fluorinated solventis used to remove the layer of fluorinated material 110. For example,perfluorodecalin (PFD) can be used as the fluorinated solvent in someembodiments of the current invention. Embodiments of the currentinvention can also include exposing the intermediate structure 112 to atleast one of a material or radiation to cause at least one of a chemicalor structural change to a portion of the intermediate structure 112. Thebarrier layer 110 substantially protects the layer of the material 102from chemical and structural changes during the exposing.

In FIG. 1, a conductive silicon wafer 106 on which silicon dioxide 108and an organic semiconductor film (pentacene) 102 were deposited wasfurther supplied with a spincoated CYTOP film 110. The CYTOP film 110was then removed by immersion in perfluorodecalin. Gold electrodes 144,116 were vacuum evaporated onto the organic semiconductor film 102through a shadow mask to complete the formation of a transistor. FIG. 1Aillustrates another example of a method of producing a spatiallypatterned structure according to an embodiment of the current invention.This example includes photolithographic steps and subsequent processingthat can be used in some embodiments of the current invention. FIGS. 2Aand 2B show output curves for pentacene OFETs (FIG. 2A) control samplesand (FIG. 2B) after CYTOP and PFD treatment described above in referenceto FIG. 1. The curves are essentially identical, showing the lack ofdamaging effects of the CYTOP and perfluorodecalin.

The broad concepts of the current invention are not limited to only theparticular fluorinated materials mentioned above. For example, molecularsolids such as perfluoroeicosane can also be used instead of or inaddition to CYTOP in some embodiments of the current invention. The mainattributes according to some embodiments of the current invention arethat the material be soluble or subject to liftoff in a fluorinatedsolvent, insoluble in any other solvent, have a very low surface energyin order to repel overlying solutions, and be volatile so that it can besublimed. A melting point above 100° C. can be desirable in someembodiments in order to ensure thermal stability of the barrier layer aslong as it is needed.

Other examples of fluorinated materials according to some embodiments ofthe current invention include, but are not limited to, any one orcombination of the following:

-   -   Perfluoropentadecane (C₁₅F₃₂) which has a melting point of        110-113° C. and is commercially available.    -   Perfluoroeicosane (C₂₀F₄₂) which has a melting point of        164-166° C. and is commercially available.    -   Perfluorotetracosane (C₂₄F₅₀) which has a melting point of        188-190° C. and is commercially available.

At some size point, the molecule might become such a stable solid thatit would not dissolve in the fluorinated solvent, though it might stilllift off. In that case, it could also become more difficult to sublime.

There is no requirement that the barrier molecules be linear, or havethe exact C_(n)F_((2n+2)) formula, though these seem to be moreavailable and are more likely to be solids. Also, while they should bepredominantly composed of CF₂ units, incorporation of up to 20% of someother chemical functionality can be allowable in some embodiments if thesolubility property is not unduly influenced by the other functionality.For example, a compound comprising 4 CH₂ groups and 16 CF₂ groups shouldwork, but adding a COOH group would greatly alter the solubilityproperty and therefore COOH compounds (carboxylic acids) may not besuitable according to some embodiments of this invention. If a lowermelting point can be tolerated, then perfluorododecane (mp 75-77° C.)and perfluorocyclohexane (mp 51° C.) are commercially available, butwould be more difficult to handle in an evaporation/sublimation systembecause of their higher vapor pressures.

Fluorinated polymers can also be used as fluorinated materials forbarrier layers according to some embodiments of the current invention.As we described above, commercially available CYTOP can be used. Also,TEFLON-AF, commercially available from DuPont, can be used in someembodiments of the current invention. More generally, there are classesof polymers such as poly(siloxanes), poly(methacrylates),poly(acrylates), and polystyrenes that do not ordinarily have thecorrect solubility and surface properties, but could be adapted to ifthey were substituted with large enough fluorinated side groups so thatthese groups dominated the solubility and surface energy properties. Atleast eight or so fully fluorinated and saturated carbons would berequired on each monomer unit for the solubility and surface propertiesto be adequate according to some embodiments of the current invention.More than eight fully fluorinated and saturated carbons on each monomerunit can be provided according to some embodiments of the currentinvention. Monomers to make such polymers are commercially available, orcan be made using methods known in the art. The utility of any one ofthese polymers would depend on specific physical attributes, such aswhether it had a high enough Tg to form a solid film, formed a usefulspin-coatable solution, etc. Any combinations of the above fluorinatedmaterials that are suitable for the particular applications can also beused according to other embodiments of the current invention.

Fluorinated solvents according to some embodiments of the currentinvention are not limited to only PFD as described above in regard toone particular example. There are many choices of commercially availablefluorinated solvents for performing the liftoff/barrier removalprocedures. These include, but are not limited to, perfluorodecalin,perfluoro(1,2- or 1,3-dimethylcyclohexane), perfluorokerosene,perfluoro(methyldecalin), and perfluoroheptane mixed isomers, andcombinations thereof. Even a low-melting, volatile fluorinated solventcould be used at a temperature above the melting point, though thiswould be a less suitable for some embodiments because of the need tomaintain the elevated temperature. For example, a fluorinated materialthat is a solid at room temperature but a liquid at a moderatelyelevated temperature such as 50° C. can be considered as a “low-melting”solvent.

FIGS. 3 and 4 provide further examples of methods of producing spatiallypatterned structures according to some embodiments of the currentinvention. In this example we further describe large scale,lithographically patterned top contact and double gate OTFT circuitswhich have not been possible using conventional lithography methods.Also, such top contact circuits can be used as sensor arrays which wouldgreatly increase the sensitivity and selectivity as compared toconventional single organic transistor based sensors. This technique canalso be used to pattern films of biological materials.

FIG. 3 is a schematic illustration of a method of producing a topcontact transistor as an example of a spatially patterned structureaccording to an embodiment of the current invention. In this example, agold gate contact, silicon oxide gate dielectric, organic semiconductor,and CYTOP are sequentially deposited onto a substrate. The CYTOP isdeposited by spincoating followed by baking at 115 degrees C. The CYTOPis briefly surface oxidized with oxygen plasma to increase the surfaceadhesion. A photoresist is spincoated onto the CYTOP, exposed to UVlight through a mask, and developed in the conventional manner. Furtherdevelopment by washing with perfluordecalin exposes the organicsemiconductor surface where the photoresist had been removed. Metal isthermally evaporated in vacuum, forming source and drain contacts on thesemiconductor. The undesired metal, photoresist, and CYTOP are removedby immersion in acetone followed by immersion in perfluorodecalin.

FIG. 4 is a schematic illustration of a method of producing a doublegate transistor according to an embodiment of the current invention. Anadditional film of CYTOP is spincoated onto the final device producedaccording to the method of FIG. 3, and baked at 115 degrees C. Anadditional gate contact is formed by photolithographic definition as forthe source and drain electrodes of FIG. 3, except the step oftransferring the pattern to CYTOP is omitted. The gate contact is formedby thermal evaporation onto the CYTOP, and residual photoresist andundesired metal are removed by immersion in acetone. The CYTOP remainsto serve as a second gate dielectric.

FIGS. 5A-5F provide a schematic illustration of a method of producing aspatially patterned structure according to another embodiment of thecurrent invention. In FIG. 5A the first electrode material is printedand then a coat of CYTOP of sub micron thickness (˜50-500 nm) is formedon top of the first electrode. The second electrode material is thenformed close to or on top of the first electrode (bead), as illustratedin FIG. 5B. Because of dewetting from the CYTOP layer, it forms aboundary at the interface. The layer of CYTOP is then washed away with afluorinated solvent, such as PFD for example. The barrier layer of CYTOPthus assists with arranging the first and second electrodes closetogether with sub-micron resolution without them overlapping (FIG. 5C).Organic semiconductor and dielectric materials can then be formed, forexample by printing (FIG. 5D). CYTOP is then printed on top of thedielectric as a precursor for self alignment of a gate electrode (FIG.5E). Finally, a gate electrode is printed on top of the CYTOP on thedielectric (FIG. 5F).

As an alternative to the step in FIG. 5E, another material such as aninsulating polymer can be deposited in droplets and coated with CYTOP orother fluorinated material. Further droplets can be deposited, utilizingthe dewetting property of the CYTOP. Then the CYTOP can be dissolvedwith a fluorinated solvent prior to final electrode deposition. One suchexample is shown schematically in FIGS. 5G and 5H. Steps 5A-5B arerepeated in this case using the same printing alignment as used for step5A but this time using an insulating polymer such as PMMA, PS, PE etc.In this case, the dielectric can be a cross-linkable polymer or aninorganic material that replaces steps 5E-5F by 5G-5H. This is followedby washing with PFD to remove CYTOP and then printing a gate electrodeon top. Thus nanoscale alignment of the gate is made to the channelbetween the source and the drain

FIGS. 6A-6C provide a schematic illustration of a method of producing aspatially patterned structure according to another embodiment of thecurrent invention. In this example, a permanent layer of CYTOP is formedon the gate electrode and source and drain electrodes are foamed next toit by a printing process. A layer of an organic semiconductor isdeposited over the electrodes and CYTOP dielectric layer to provide thetransistor structure.

FIG. 7 is a schematic illustration of a method of producing thin-film,lateral heterojunction, organic diodes according to an embodiment of thecurrent invention. The lithographic patterning according to thisembodiment ensured that the junction was precisely in a lateralarrangement and there was essentially no overlap or mixing of the twosemiconductors. This embodiment of the current invention can alsoprovide the ability to reproducibly fabricate patterned organicsemiconductors without damage to its morphology and electronicproperties and can also leave the organic semiconductor surface open forfurther processing and/or investigation,

As an example, laterally defined heterojunctions were fabricated usingthe process steps shown in FIG. 7 according to an embodiment of thecurrent invention. A schematic illustration of a thin-film, lateralheterojunction, organic diode according to an embodiment of the currentinvention is shown in FIG. 7A. Such a diode can be made by the methodillustrated in FIG. 7; however, the structure of the diode is novelirrespective of the method of manufacture. Previous attempts atpatterning organic semiconductors had a problem that the semiconductorswere covered by a barrier layer (Kymissis method) or the removal of abarrier layer resulted in damage to the organic semiconductor (Mallairasmethod). According to an embodiment of the current invention,fluorinated barrier layers that are soluble only in fluorinated solventsare used. These are completely orthogonal to any other non-fluorinatedor partially-fluorinated material. Here both CYTOP and perfluoroeicosanecan be used interchangeably, for example, with the flexibility that theformer can be spin coated and the latter can be thermally evaporatedunder high vacuum. This technique is a general method that can be usedto pattern other soft matter films using photolithography whileretaining the functional properties of the film.

In this example, a 50 nm 5FPE-NTCDI film was thermally evaporated in ahigh vacuum chamber at a substrate temperature of 120 degree C. toobtain good morphology and electrical characteristics. (The common term5FPE-NTCDI refers toN,N′-bis(2-(pentafluorophenyl)ethyl)naphthalene-1,4,5,8-tetracarboxylicdiimide.) After patterning the NTCDI film the P3HT film was spin coatedfrom solution in 1, 2 dichlorobenzene (10 mg/ml) at 1500 rpm for 90seconds. (The common term P3HT stands for regioregularpoly(3-hexylthiophene).) After fabricating the lateral heterojunction,gold electrodes were evaporated (in a vacuum chamber) as top contactsusing a metal shadow mask with separation of 200 μm. The substrates usedwere highly doped silicon wafers with 300 nm thermally grown SiO₂.

We have measured diode characteristics for different semiconductorcombinations as a function of doping one OSC and as a function of gatebias according to some embodiments of the current invention. We show thetuning of the rectification ratio by the application of gate voltage byalmost two orders of magnitude.

In order to confirm that the electrical quality of the lithographicallyprepared junction was good, we prepared samples with P3HT spin coated onboth sides but with different film qualities. The first film was spincoated from a 10 mg/ml solution of P3HT in 1, 2 dichlorobenzene at 1500rpm. The second film was spin coated from a 6 mg/ml solution of 1, 2dichlorobenzene at 800 rpm. The remaining steps in the processing werethe same as described above. FIG. 8 shows transfer characteristics ofthe junction vis-a-vis the individual films. The first film had bettercharacteristics than the first one because of processing and annealingfor 30 min in N₂ in a glove box at 120 degree C. No annealing treatmentwas done after the fabrication of the junction and hence the second filmhas lower performance as compared to the first one. As expected, thetransfer characteristics of the junction are intermediate to that of theindividual films. This control experiment clearly illustrates that theelectronic quality of the junction is good even without the annealingtreatment and the lithographic patterning technique does not causedamage.

FIGS. 9-16 show data for two examples of thin-film, lateralheterojunction, organic diodes according to an embodiment of the currentinvention. The diodes according to this embodiment of the currentinvention have thin films of p- and n-channel organic semiconductorsformed laterally and in contact at a p-n heterojunction on asubstructure. The substructure can include a substrate and dielectriclayer, for example. The diode has a first electrode attached to thep-channel semiconductor and a second electrode attached to the n-channelsemiconductor. In some embodiments, the thin-film, lateralheterojunction, organic diode can have a third electrode arrangedproximate the p-n heterojunction to selectively adjust the electricfield at the p-n heterojunction. For example, the substrate can providethe third electrode in some embodiments (See FIG. 7A for an example of ahighly doped Si substrate as the third electrode that has a SiO₂ layerto provide a dielectric layer between the third electrode and thelateral semiconductor layers). However, one of ordinary skill in the artshould recognize, based on the teachings herein, that numerousalternative structural arrangements are included within the generalconcepts of the current invention.

In another example according to an embodiment of the current invention,a diode was produced according to the method illustrated schematicallyin FIG. 7. This shows the process flow diagram for lithographicfabrication of a lateral heterojunction using CYTOP as a barrier layerand perfluorodecalin as a selective solvent. We used P3HT as thep-channel organic semiconductor material and F16CuPc as the n-channelorganic semiconductor material. (The term F16CuPc stands for copperhexadecafluorophthalocyanine.) Gold electrodes were either deposited astop contacts by shadow masking after fabricating the heterojunction orpre-patterned lithographically in a bottom contact configuration. Thesubstrates used were highly doped silicon wafers with 300 nm thermallygrown SiO₂. An 80 nm F16CuPc film was thermally evaporated in a highvacuum chamber at a substrate temperature of 120° C. After patterningthe F16CuPc film, the P3HT film was spin coated from solution inchlorobenzene (8 mg/ml) at 1500 rpm for 60 seconds. FIG. 17 shows thediode characteristics of this lateral diode.

In conclusion, we have demonstrated working lateral heterojunctionsaccording to some embodiments of the current invention usingphotolithographic methods of production according to an embodiment ofthe current invention. The method in itself is general and can beapplied to pattern films of soft materials (small molecules, polymers,biological films) without damage to structural form and functionality.This is the first demonstration of a lateral diode based on organicsemiconductors which can be electrostatically doped to alter its builtin potential difference and hence change it performance characteristics.However, methods of manufacture and devices according to embodiments ofthe current invention are not limited to specific examples described.

In describing embodiments of the invention, specific terminology isemployed for the sake of clarity. However, the invention is not intendedto be limited to the specific terminology so selected. Theabove-described embodiments of the invention may be modified or varied,without departing from the invention, as appreciated by those skilled inthe art in light of the above teachings. It is therefore to beunderstood that, within the scope of the claims and their equivalents,the invention may be practiced otherwise than as specifically described.

1-21. (canceled)
 22. A spatially patterned structured produced accordingto a method comprising: forming a layer of a material on at least aportion of a substructure of said spatially patterned structure; forminga barrier layer of a fluorinated material on said layer of material toprovide an intermediate structure; and exposing said intermediatestructure to at least one of a second material or radiation to cause atleast one of a chemical change or a structural change to at least aportion of said intermediate structure, wherein said barrier layersubstantially protects said layer of said material from chemical andstructural changes during said exposing.
 23. A diode, comprising: asubstructure; a thin film of an n-channel organic semiconductor formedon said substructure; a thin film of a p-channel organic semiconductorformed on said substructure in a position laterally displaced from saidthin film of said n-type organic semiconductor so as to form a p-nheterojunction in a lateral arrangement on said substructure.
 24. Adiode according to claim 23, further comprising: a first electrode inelectrical contact with said thin film of said n-channel organicsemiconductor at a position displaced away from said p-n heterojunction;and a second electrode in electrical contact with said thin film of saidp-channel organic semiconductor at a position displaced away from saidp-n heterojunction.
 25. A diode according to claim 24, furthercomprising a third electrode arranged proximate said p-n heterojunction,wherein said third electrode is suitable to control an electric fieldwithin region proximate said p-n heterojunction.
 26. A diode accordingto claim 23, wherein said substructure comprises a substrate.
 27. Adiode according to claim 26, wherein said substrate is a flexiblesubstrate.